This invention relates to computer systems, and more particularly to devices for interconnecting input-output (I/O) equipment to computer system processors. The invention also contemplates the interconnection of multiple processors, and the use of an emulated I/O adapter to economically expand the access to and use of computer processor I/O channels.
Conventional computer architecture utilizes one or several computer processors connected to internal memory devices and other logic, and has one or more I/O channels for transferring information, commands and controls to devices external the processor. A typical example of conventional architecture is a computer processor having a high-speed memory, and having an I/O channel which is connected to various hardware adapters to external memory sources, printers, communications lines, and other devices which are important to overall system operation but which are remotely located from the processor. Communications through the I/O channel are conducted according to a predetermined format of signal transmission, wherein the computer processor may selectively address and activate any of the devices wired to the channel. The devices are wired to respond to predetermined address information, and to interchange signals with the processor according to the predetermined format selected for the particular system.
Because of physical and electrical differences between the various devices on a processor I/O channel and the processor itself, it is usually necessary to interpose an adapter between the device and the channel electronics. An example of such an adapter is a disk controller, which is a specially designed package for interfacing with the electrical signals on the processor I/O channel on the one hand, and for interfacing with the magnetic media electrical circuit requirements of the disk on the other hand. A further example of an adapter is a communications adapter or modem, which accepts processor signals from an I/O channel and converts them to electrical signals suitable for transmission over telephone lines.
Particularly on more sophisticated computer systems, the I/O adapters required for handling various I/O devices are relatively complex and expensive to construct, for it is frequently required that they incorporate a predetermined minimum level of intelligence in the form of logic circuits within their design, so as to impose only a nominal loading effect upon the processor when they are activated. By contrast, I/O devices may be connected to smaller computers, such as computers which have become known as "personal computers", through adapters which are significantly less complex and sophisticated, for the loading penalty imposed upon the personal computer is relatively less expensive.
It is therefore desirable to provide an adapter of simple design and low cost which can enable the interconnection of smaller computers, such as personal computers, into the I/O channel control link to more sophisticated computers, and to thereby provide for the possibility of utilizing a personal computer as an element for subsequent control and connection to further I/O devices.